We have a 2006 beta rev 80 it's underpowered for our 14 year old who is slightly built but perfect for our youngest son who's nearly 11.
Our 14 year easily rides our ossa 280 with careful throttle control though.
A 125 would be the best buy for two years of ownership for a 14 year old although a beta rev 125 is not as powerful as a beta evo 125 for example.
Good Luck !
Ossa really easy to ride can't get my 13 year old son off our 280 so much so sold his beta 80.
Got to be fitted with an easy start system most are now just a button on the bars.
Great value for money 6 months old for £3000
The uk importer has a 2013 brand new at £4500 see ossa uk on google
both good enough to get out on.
we had two beta minitrial old and new model never had a reliability problem-the gas gas 50 was a different story sold it for parts in the end.
another good bike is yamaha ty80 but it has a clutch although doesn't take to long to learn to pull clutch in to stop and let it out slowly to start off.
Ossa yes fuel injection which means no carb to clean out,50-1 fuel ratio so less oil to buy and burn-our local dealer said gearbox oil about once a year-have had no problems whatsoever in two years-heard the 2011 model had some teething problems though.
Frankly all models a pretty good just what takes your eye.
I went for Ossa as technically ahead of the rest in design especially the exhaust design out of the rear of the engine direct to the rear silencer-front exhaust exit is the same as my Dad`s 1960`s Triumph Tiger Cub.
Anyway good luck in the search.
All depends on your budget I have a montesa 315 it's 15 years old still going strong and about £1000 will get something to get out can't be compared to a late bike from any manufacturer though.
Leave the opinions on other bikes to other members !